I. Field of the Invention
This invention relates generally to a method for prescribing an exercise regimen for a particular subject, and more particularly to a method for correlating a heart rate or work rate to be maintained throughout an exercise session if the desired goal of the exercise is to reduce fat or to improve cardiovascular performance
II. Discussion of the Prior Art
It is well recognized that frequent exercise is beneficial to most individuals so long as it is properly engaged in, taking into account the individual's own physiologic condition It is important that the exercise regimen not be so intensive that it adversely affects the general well being of the subject, yet not too light that it provides little or no benefit.
It is well understood that with increasing exercise, muscles need to burn metabolic fuels to perform mechanical work Carbohydrates and fat are the typical sources of fuel and must be oxidized, using molecular O.sub.2 from the atmosphere to effectively provide energy. A normal response to exercise is to increase the blood flow to the working muscles which carries oxygen and removes carbon dioxide, the bi-product of biologic metabolism. The increasing demands for oxygenated blood are met by increasing the cardiac output (increased heart rate and increased stroke volume) and redistributing the blood flow to the working muscles and away from the abdominal area.
As a consequence of the need for more oxygen and the increased production of carbon dioxide, the level of ventilation must also increase. More air is taken in, in order to oxygenate the increased amount of blood going through the lungs and to eliminate the increased amount of carbon dioxide being brought to the lungs from the working muscles Ventilation normally increases in direct linear fashion with CO.sub.2 output rather than oxygen uptake (VO.sub.2) such that the arterial carbon dioxide tension remains constant during aerobic work.
The heart rate also increases in a linear fashion with increasing VO.sub.2 and the maximum heart rate is limited in any individual by age.
When the supply of oxygenated blood falls short of the oxygen needs of the muscles, anaerobic metabolism ensues. The bi-product of anaerobic metabolism is lactic acid, which is buffered by the bicarbonate system. Additional CO.sub.2 is produced which must be eliminated by the lungs to keep arterial carbon dioxide tension from rising. Carbon dioxide output (VCO.sub.2) will be increased relative to VO.sub.2. This will be seen in graphic form as an increase in CO.sub.2 output and ventilation with respect to oxygen uptake. Since the respiratory exchange ratio (RER) is the ratio of VCO.sub.2 to VO.sub.2, that ratio will also be seen to increase, often to values greater than 1.
Individualized training programs must satisfy the basic goals of safety and effectiveness. Safety dictates that exercise be formed at the minimum effective heart rate whereas effectiveness dictates that the exercise program must result in the accomplishment of a desired goal, such as fat loss and improved cardiovascular fitness. In the past, many health professionals and some exercise equipment manufacturers use the so-called Karvonen method for determining what the heart rate should be during the exercise program if either fat burning or cardiovascular conditioning is the desired goal. In accordance with the Karvonen method, to determine the target heart rate to be maintained during a period of exercise to enhance fat burning, the following formula is commonly used: EQU Target heart rate=220-age-0.6.times.resting pulse rate+resting pulse rate
Likewise, for cardiovascular conditioning in accordance with the Karvonen method, the following formula is utilized: EQU Target heart rate=220-age-0.8.times.resting pulse rate
Use of the above formulas generally results in target heart rates which are too high to achieve fat reduction or higher than necessary to achieve improvements in cardiovascular fitness. Higher than necessary intensity of exercise, of course, impacts not only safety and efficacy, but also compliance. Because the high intensity of exercise results in the painful accumulation of lactate and depletion of muscle glycogen, individuals will not be able to comply with programs which specify high work intensities, such as those specified using the Karvonen predicted heart rates and exercise will be discontinued without achieving the desired goal.
When one exercises, there are several requirements which must be met in order for the exercising muscles to perform work. At low levels of exercise, such as walking at a modest rate, the exercising muscle must have oxygen and fuel to produce energy. The two types of fuels are fats and carbohydrates. The intensity of exercise dictates which fuel will be utilized during any type of exercise. Since carbohydrates tend to be a substantially more efficient fuel, it is the body's carbohydrates that are consumed during exercise at higher levels of intensity. Fat, being a less efficient fuel, tends to be consumed by the body when exercising at relatively low levels of intensity. Therefore, if a person exercises at too high of a heart rate, fat burning objectives will not be realized.
By monitoring the Respiratory Exchange Ratio (RER), it is possible to determine which type of fuel is being utilized at any given time. It is found that the closer that the RER is to 0.7, the greater the fat utilization. Contrariwise, the higher the intensity of exercise, the greater is the utilization of carbohydrates. By simultaneously monitoring the RER and the heart rate, it becomes possible to clearly identify the heart rate at which fat is the preferred fuel. It is commonly found that in unfit individuals, this is often at a surprisingly low level of work. In more fit individuals, fat will continue to be used as a fuel for longer periods. While exercise at a intense rate may cause a temporary weight loss due to a reduction in body water from sweating, we have determined that an exercise program designed to maximize the elimination of fat should be based upon activities and exercise where the heart rate is confined to a zone corresponding to the heart rate at a computed fat burning point .+-.10%. The fat burning point is computed as the valley in the RER curve or the lowest point where the respiratory exchange ratio is determined to be less than 0.90 and oxygen consumption is less than 55% of the peak oxygen uptake.
We have determined that for optimum cardiovascular improvement, exercise should be maintained in a zone such that the heart rate is maintained at the value at the anaerobic threshold plus 20%. While carbohydrates would be the fuel that is exclusively utilized at levels of exercise in this latter zone, there still exists certain benefits even for those desiring to lose fat. By improving cardiovascular fitness, the basal metabolic rate for the individual will increase. By increasing the basal metabolic rate, the number of calories that an individual routinely uses in activities of daily life increases. Interestingly, daily activities typically fall into the low intensity category in which fat is used as a fuel. So, by performing this higher intensity training on a regular basis, it is possible to improve fitness and have positive impact on fat loss.
In the Anderson et al. U.S. Pat. No. 4,463,764, there is described a computerized exercise testing system which allows a breath-by-breath analysis of the kinetics of O.sub.2 uptake, CO.sub.2 output and minute ventilation on a real-time basis during exercise. Using that equipment, it is possible to compute the respiratory exchange ratio and, from that, to determine the range of heart rates to be maintained during exercise if fat consumption is the goal. Moreover, that same equipment may be used to determine the anaerobic threshold and the heart rate existing at that point. Thus, using this data, the invention is able to compute the range of heart rates or work rates for enhancing fat loss and cardiopulmonary performance.